how old.. how big?? soil??? whats the weather been .. drought or torrential rains ???? what are other trees in the 'hood' doing... other trees stressed? more facts will give a better answers ... ken

Karyn, so you have a good sized GH? I am getting materials together to build one, but I was probably shooting for something like 6x8, maybe 8x8? If these trees alone are in big pots, that would fill up the space...How big of a pot do these really need to be in to give them the space they need to grow properly? Has anyone ever used something like a free standing individual greenhouse like covering? I had read something about this recently, where you could basically erect a GH when needed to protect specific plants/trees etc when there was going to be frost then take it down again. It was built with some kind of pole like frame that was put into permanent "supports" that are actually left in the ground near the tree all the time and then they used some kind of plastic and put up a cover for the tree? I guess I'll try to search again and find the info and post it as a new question...

In the heat of the summer, some yellowing due to all forms of heat stress is expected. Down here for example, we are still in summer mode; we just hit 95 degrees yesterday. Buuuuuuuuuut in northern IL at this time of the year, I expect hydrangeas to be in shut down mode. Yours are obviously ahead of the neighbor's hydrangeas but not a big deal. The green leaves will then turn yellow, brown out and fall down. Or if a dip below freezing happens, some green leaves will actually look dark green ugly and then turn brown. You can let the brown leaves drop down on their own if you have no fungal issues. If you do have fungal issues, you can throw them into the trash instead. You can leave the spent blooms for Halloween/winter interest or deadhead them whenever you want. As usual, maintain 3-4" of mulch in preparation for winter and -still- keep the soil as evenly moist as you can for now. Once the plant goes dormant, you can reduce waterings down to once a week or once every two weeks but stop waterings when the soil freezes. This year is expected to be warmer than normal due to El Nin~o on the northernmost states. They say it will be the strongest one in 50 years so maybe try to read up on what to expect weather-wise in IL. Wild temp changes may "awaken" some dormant plants and this would especially negatively affect any mopheads, oakleaf and lacecap hydrangeas. Their stems and invisible flower buds may get zapped if not winter protected. So if you have any of those, consider using winter protection. VS, being a paniculata, will not need winter protection as panics care usually hardy to Zone 3 and develop invisible flower buds in late Spring or early Summer... but I mention it just in case you also have some of the other hydrangeas.

Has your tree been getting enough water? If you recently dug up the tree and replanted it, that could likely have compromised its root system and made it difficult for the tree to uptake adequate water, even if the soil is soaking wet. New leaflets turning brown often means the plant either does not have adequate water or vigor to sustain their continued growth.